Scanning system for touch screen keyboards

Abstract

A touch screen control system having a plurality of light emitter and detector pairs positioned on opposite sides of a touch screen display. The emitters and detectors are controlled by a microprocessor-based control system that energizes each of the light emitters in a pseudorandom manner. Before each light emitter is energized, the intensity of ambient light is measured by its associated light detector, and the ambient temperature is also measured by a temperature sensor. The intensity at which the light emitter is then energized is controlled as a function of ambient light and temperature. The control system generates a bitmap identifying beams from each light emitter to its associated detector that are obscured during each of several scans of the light emitter/detector pairs. In order to reject false receptions of light from an obscured light emitter beam, the control system processes the bitmap through a predetermined voting procedure. The control system is thus able to minimize the effect of interfering light sources on the performance of the touch screen.

I claim: 
     
       1. A touch screen keyboard system for a display panel, comprising: a plurality of spaced-apart light emitters positioned along at least one edge of said display panel;   a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters;   power means for selectively energizing each of said light emitters in response to an activation signal applied to each of said light emitters;   detector means for enabling an output form at least one predetermined light detector while a respective light emitter is being energized, and for determining whether light from the energized light emitter is being received by said enabled light detector; and   control means for generating a pseudo random activation signal for each of said light emitters thereby energizing said light emitters in the pseudo random manner to reduce the probability that an external light source operating in close proximity will operate in synchronism and thus interfere with said touch screen.   
     
     
       2. The touch screen keyboard system of claim 1 wherein said display panel is rectangular, and wherein said light emitters are positioned along two adjacent edges of said panel, and said light detectors are positioned along the two remaining edges of said panel. 
     
     
       3. The touch screen keyboard system of claim 1 wherein only one of said light detectors is enabled while a respective light emitter is being energized. 
     
     
       4. The touch screen keyboard system of claim 3 wherein each of said light emitters is positioned opposite a corresponding one of said light detectors, and wherein the light detector corresponding to a respective light emitter is enabled while said light emitter is energized. 
     
     
       5. A touch screen keyboard system for a display panel, comprising: a plurality of spaced-apart light emitters positioned along at least one edge of said display panel to form part of said touch screen keyboard system;   a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters to form part of said touch screen keyboard system;   power control means for selectively energizing each of said light emitters in response to an activation signal applied to each of said light emitters, said power control means energizing each of said light emitters at an intensity corresponding to a respective intensity control signal;   detector means for enabling an output from at least one predetermined light detector while a respective light emitter is being energized, and for determining whether light from the energized light emitter is being received by said light detector; and   compensation means for generating each of said intensity control signals as a function of the intensity of ambient light so that the intensity of light emitted by said light emitters is a function of the intensity of ambient light.   
     
     
       6. The touch screen keyboard system of claim 5 wherein said system further includes a temperature sensor for generating a temperature signal indicative of the temperature of ambient temperature, and wherein said compensation means receives said temperature signal and adjusts said intensity control signals as a function of the ambient temperature indicated by said temperature signal. 
     
     
       7. The touch screen keyboard system of claim 5 wherein said ambient light is measured by at least one of said light detectors, and wherein each of said light detectors is enabled before and after a respective light emitter is being energized. 
     
     
       8. The touch screen keyboard system of claim 5 wherein said power control means comprise voltage to current converting means connected in series with each of said light emitters, said voltage to current converting means receiving said intensity control signals and causing current to flow through said light emitters as a function of the magnitude of said intensity control signals upon receipt of said activation signal. 
     
     
       9. The touch screen keyboard system of claim 8 wherein said compensation means comprise: a processor having a first I/O port receiving data indicative of the intensity of ambient light, and a second I/O port outputting data indicative of the magnitude of said intensity control signal;   a digital-to-analog converter connected to the second I/O port of said processor, said digital-to-analog converter generating at an output said intensity control signal having a magnitude corresponding to the data output from the second I/O port of said processor; and   a multiplexer connected between said digital-to-analog converter and said power control means, said multiplexer being controlled by said processor to selectively apply the output of said digital-to-analog converter to the power control means for each of said light emitters.   
     
     
       10. The touch screen keyboard system of claim 5 wherein said compensation means for generating each of said intensity control signals comprises: a processor receiving data indicative of the intensity of ambient light and generating a first digital word indicative of the desired intensity of light to be emitted by said light emitters; and   a digital-to-analog converter connected to said processor, said digital-to-analog converter receiving said first digital word and generating at an output an analog signal corresponding thereto from which said intensity control signals are generated.   
     
     
       11. The touch screen keyboard system of claim 10 further including a multiplexer having an input and a plurality of outputs that are selectively connected to said input responsive to a second digital word, the input of said multiplexer being connected to the output of said digital-to-analog converter to receive said analog signal therefrom, the outputs of said multiplexer being connected to said power control means, and said second digital word being received from said processor so that said multiplexer outputs said intensity control signals to control the intensity of light emitted by respective of said light emitters. 
     
     
       12. The touch screen keyboard system of claim 10 wherein said compensation means further includes a one-shot for gating said intensity control signals to said power control means for a predetermined duration. 
     
     
       13. The touch screen keyboard system of claim 12 wherein said one-shot comprises: a counter having a reset input receiving an enable input from said processor, a clock input, and a multibit output generated on respective output terminals for providing a digital word indicative of the count of said counter; and   a first gate having an output coupled to the clock input of said counter, said first gate having a first input receiving a clock signal, and a second input receiving a disable signal from a first output of said counter so that said first gate is disabled when the logic level of said first output changes thereby preventing said clock signal from reaching the clock input of said counter whereby said counter is incremented by said clock signal upon receipt of said enable signal until the logic level of the signal on said first output changes state thereby preventing said clock signal from continuing to increment said counter, whereby said first output of said counter is used to gate said intensity control signals to said power control means for a predetermined duration.   
     
     
       14. A touch screen keyboard system for a display panel, comprising: a plurality of spaced-apart light emitters positioned along at least one edge of said display panel;   a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters;   power means for selectively energizing each of said light emitters in response to an activation signal applied to each of said light emitters;   detector means for enabling at least one predetermined light detector while a respective light emitter is being energized, and for determining whether light from the energized light emitter is being received by said enabled light detector;   control means for straining said light emitter/light detector pairs by generating an activation signal for each of said light emitters;   memory means connected to said detector means to record whether light from each of said light emitters is being received by a respective light detector during a predetermined number of scans of said light emitter/light detector pairs; and   processing means operatively connected to said memory means for providing an indication that an area of said display panel corresponding to a predetermined light emitter/light detector pair has been activated only if light from the light emitter in said pair has not been received by the respective light detector in said pair during a plurality of successive scans of said light emitter/light detector pairs.   
     
     
       15. A method of scanning a touch screen keyboard system having a plurality of spaced-apart light emitters positioned along at least one edge of a display panel and a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters, said method comprising: pseudo randomly energizing each of said light emitters, and   determining if light from each energized light emitters is being received by a corresponding light detector so that the probability that a plurality of touch screen keyboard systems operating in close proximity will operate in synchronism and thus interfere with each other is reduced.   
     
     
       16. The method of claim 15 wherein each of said light emitters is positioned opposite a corresponding one of said light detectors, and wherein the light detector corresponding to a respective light emitter is enabled when said light emitter is energized. 
     
     
       17. A method of scanning a touch screen keyboard system having a plurality of spaced-apart light emitters positioned along at least one edge of a display panel and a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters, said method comprising: selectively energizing each of said light emitters at an intensity that is a function of the intensity of ambient light;   enabling an output from at least one predetermined light detector while a respective light emitter is being energized; and   determining whether light from the energized light emitter is being received by said enabled light detector.   
     
     
       18. The method of claim 17 further including the steps of: determining the ambient temperature of said touch screen; and   further adjusting the intensity at which said light emitters are energized as a function of the ambient temperature.   
     
     
       19. A method of scanning a touch screen keyboard system having a plurality of spaced-apart light emitters positioned along at least one edge of a display panel and a plurality of spaced-apart light detectors positioned along an edge of said display panel opposite said light emitters, said method comprising: selectively energizing each of said light emitters;   enabling an output from at least one predetermined light detector while a respective light emitter is being energized;   determining whether light from the energized light emitter is being received by said enabled light detector;   recording whether light from each of said light emitters is being received by a respective light detector during a predetermined number of scans of said light emitter/light detector pairs; and   providing an indication that an area of said display panel corresponding to a predetermined light emitter/light detector pair has been activated only if light from the light emitter in said pair has not been received by the respective light detector in said pair during a plurality of successive scans of said light emitter/light detector pairs.